Touch sensing technology capable of providing a natural interface between an electronic system and user has found widespread applications in a variety of fields, for example, in mobile phones, personal digital assistants (PDAs), automatic teller machines (ATMs), game machines, medical devices, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, computing devices, and the like, where a user may input desired information and/or operate the electronic system through a touch sensing device associated with the electronic system. A touch sensing device typically includes a controller, a sensing circuit having a plurality of touch sensors and a network of control lines electrically connecting the plurality of touch sensors to the controller, and a touch panel associated with the plurality of touch sensors.
There are different types of touch sensing devices available for detection of a touch location. One is a resistive-type touch sensing device that includes two layers of transparent conductive material, such as a transparent conductive oxide, separated by a gap. When touched with sufficient force, one of the conductive layers flexes to make contact with the other conductive layer. The location of the contact point is detectable by a controller that senses the change in resistance at the contact point. In response, the controller performs a function, if any, associated with the contact point.
Another one is a capacitive-type touch sensing device. The capacitive-type touch sensing device can be classified into two types: an analog capacitive sensing device, which uses a contiguous resistive layer, and a mutual-type projected capacitive sensing device, which uses patterned conductive layers (electrodes).
In a projected capacitive touch device, the touch sensor employs a series of patterned electrodes that are driven with a signal from a controller. Similarly, a location of the contact point can be derived from currents flowing through one or more corresponding electrodes toward the touch point responsive to the touch with sensing the capacitance induced by a user's finger. A finger touch to the sensor provides a capacitive couple from the conductive layer to the body. The location of the contact point is detectable by a controller that measures a change in a capacitively coupled electrical signal at the touch location. Accordingly, the controller performs a function, if any, associated with the touch location.
FIG. 12 shows a conventional capacitive touch device 10 having five (5) driving electrodes X1-X5, and ten (10) sensing electrodes Y1-Y10 arranged in a 5×10 matrix. Traditionally, a driving signal 16 is applied to a single driving electrode, for example, X2. The driving signal 16 is, through a mutual capacitance coupling, transmitted to a sensing electrode, for example, Y6. Meanwhile, the other driving electrodes, X1 and X3-X5 and the other sensing electrodes Y1-Y5 and Y7-Y10 are grounded. For such a driving method, a lot of capacitance is generated between the driving electrode (X2) and all the sensing electrodes (Y1-Y10), which is indicated by Cm, and between the driving electrode (X2) and its neighboring driving electrodes X1 and X3, which is indicated by Cd. For a large sized touch panel, the capacitance causes significant increase of the RC loading between electrodes, thereby resulting in deformation of the signal output. As shown in FIG. 12, the driving signals 18 and the sensing signals 17 of sensing electrodes in distal areas are substantially deformed, comparing to a driving signal 16 applied to a driving electrode, due to the RC loading of the driving electrodes X2 and/or sensing electrodes Y1-Y10. The larger the touch panel is, the worse the deformation of the sensing signals is. The deformation of the sensing signals may result in poor performance of the touch panel.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.